Various type chemical processes are commonly carried out in large, stirred vessels which are frequently provided with auxiliary equipment, such as baffles, agitator equipment, heat transfer coils which enable heat to be supplied or extracted from the contents of the vessels, and the like. In many cases, however, such processes eventually produce undesirable deposits on the surfaces of the equipment with which the reaction mixtures come into contact. Such deposits interfere with the efficient transfer of heat to and from the interior of the vessels. Further, these deposits have a tendency to deteriorate and to partially fragment resulting in contamination of the reaction mixture and the products produced therefrom. This problem is particularly prevalent in polymerization type reactions, since the deposits, or buildup, of solid polymer on reactor surfaces, not only interferes with heat transfer, but decreases productivity and adversely affects polymer quality.
The polymer buildup problem is particularly troublesome in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal ##STR2## or with polymerizable polyolefinic monomers. For example, when polymerizing vinyl chloride, and other comonomers when used, the same are maintained in the form of discrete droplets in an aqueous suspension system by the use of suspending agents and agitation. When the reaction is complete, the resultant polymer, or PVC, is washed and dried. However, these suspension systems are often unstable and during the polymerization reaction, vinyl chloride polymer builds up on the interior surfaces of the reactor, including the surfaces of the baffles and agitator. Obviously, this polymer buildup must be removed since it results in further formation of polymer buildup which in turn results in a crust that adversely affects heat transfer and contaminates the polymer being produced. While various methods have heretofore been proposed to reduce the amount and nature of polymer buildup on polymerization reactor surfaces, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like, none has proved to be the ultimate in polymer buildup removal. That is to say, these various methods and apparatus have done an acceptable job, but there is still room for improvement in this area, particularly from an economic point of view.
It has been proposed to coat the internal surfaces of the reactor with various polymer buildup resistant coating materials. For example, in U.S. Pat. Nos. 4,024,330 and 4,024,301, various polyaromatic amines are shown as useful for coating reactors to substantially eliminate buildup. Alkali soluble dyes have been shown to be useful for this purpose in U.S. Pat. No. 4,068,059. Further, in U.S. Pat. No. 4,080,173 there is shown and described the use of selfcondensed polyhydric phenols and polyhydric naphthols as useful coating materials to prevent polymer buildup. While all these coating materials give good to excellent results, the search continues for new and improved polymer buildup resistant materials with which to coat reactors for the purpose of preventing or eliminating polymer buildup on the inner surfaces thereof.